1. Field of the Invention
The present invention relates to a leak reducing structure in a steam turbine. More particular, it relates to a leak reducing structure in a steam turbine, which prevents a trouble such that in a steam turbine of a single casing type, high-pressure steam passes through a seal portion of a dummy ring and leaks to the intermediate pressure turbine side, by which the performance is decreased.
2. Description of Related Art
FIG. 3 is a sectional view showing the interior of a conventional steam turbine of a single casing type. In FIG. 3, reference numeral 1 denotes a rotor, 2 denotes an external casing covering the whole of the turbine, 3 denotes a high pressure turbine section in which stator blades on the stationary side and rotor blades fixed to the rotor 1 are arranged in a multi-stage form, 4 denotes an intermediate pressure turbine section in which stator blades and rotor blades are arranged in a multi-stage form in the same way, and 5 denotes a similar low pressure turbine section. These high pressure, intermediate pressure, and low pressure turbine sections 3, 4 and 5 are arranged around the rotor 1 in the axial direction thereof in the single external casing 2.
A high-pressure steam inlet port 6 supplies high-pressure steam to the high pressure turbine section 3, and a high-pressure steam outlet port 7 causes the steam that has done work in the high pressure turbine section 3 to flow out to the outside. Also, an intermediate-pressure steam inlet port 8 supplies intermediate-pressure steam to the intermediate pressure turbine section 4, and a low-pressure steam inlet port 9 supplies low-pressure steam to the low pressure turbine section 5. A nozzle chamber 13 for high-pressure steam is integrally incorporated in a dummy ring 10. The dummy ring 10 is disposed between the high pressure turbine section 3 and the intermediate pressure turbine section 4 to provide a seal. The steam that has done work in the intermediate pressure turbine section 4 and the low pressure turbine section 5 is discharged to an exhaust chamber 11.
In the steam turbine of the above configuration, high-pressure steam 30 flows into the high pressure turbine section 3 through the high-pressure steam inlet port 6, does work in the high pressure turbine section 3, and flows out through the high-pressure steam outlet port 7. Also, intermediate-pressure steam 32 flows into the intermediate pressure turbine section 4 through the intermediate-pressure steam inlet port 8, and does work in the intermediate pressure turbine section 4. Thereafter, the steam further flows into the low pressure turbine section 5. Low-pressure steam 33 flows into the low pressure turbine section 5 through the low-pressure steam inlet port 9. In the low pressure turbine section 5, the steam flowing from the intermediate pressure turbine 4 and the steam flowing through the low-pressure steam inlet port 9 are combined to do work, and are discharged to the exhaust chamber 11.
In the turbine of the above configuration, the rotor 1 is rotated in the high pressure turbine section 3, the intermediate pressure turbine section 4, and the low pressure turbine section 5 as described above, by which a generator (not shown) connected to the rotor 1 is rotated. Between the high pressure turbine section 3 and the intermediate pressure turbine section 4, there is disposed the dummy ring 10 to provide a seal. Therefore, some of the high-pressure steam passes through a seal portion of the dummy ring 10, and causes a leak to the side of the intermediate pressure turbine section 4 as a leak 34, resulting in a decrease in performance.
As described above, in the steam turbine comprising the high pressure, intermediate pressure, and low pressure turbine sections in the single casing, the dummy ring 10 for providing a seal is provided between the high pressure turbine section 3 and the intermediate pressure turbine section 4, and some of high-pressure steam from the high pressure turbine section 3 passes through the seal portion of the dummy ring 10, causing a leak to the side of the intermediate pressure turbine section 4. Therefore, if the leak amount is large, the performance is affected adversely, so that there is a fear of decreasing the performance of the high pressure turbine section 3.